1. Field of the Invention
The present invention relates to a method for producing an optical member. The optical member of the present invention may be disposed, for example, in a windshield for cars, etc. and may be applied to a display panel in a heads up display device.
2. Related Arts
A hologram film has been used as an optical member, especially as a thin filmy optical member. A hologram film is obtained by exposing a photosensitive film to light to form interference fringes which create the holographic image. Since such a hologram film is flexible and is extremely thin, it can be sealed, for example, in a windshield for cars, etc. to be used as a display panel in a heads-up display device.
In order to obtain a high-quality display image, the hologram film must be stuck onto the glass substrate without being wrinkled or forming a gap between itself and the glass substrate. For mounting on cars, for example, as a member of a heads-up display device, the hologram film must have satisfactory heat resistance.
Where the hologram film is stuck onto a support plate, such as a windshield glass, etc., an optical adhesive may be used. A semi-curing acrylic adhesive, for example, has been used the optical adhesive. The adhesiveness of such an adhesive is not completely cured. Such a semi-curing acrylic adhesive can be coated thin onto a substrate by spin coating. Also, since the adhesive is sticky, it can be used for sticking a hologram film onto a support plate without wrinkling the film or forming a gap between the film and the support plate.
However, the adhesive has the following problems with regard to heat resistance.
When a semi-curing acrylic adhesive is exposed to a high-temperature atmosphere at 80.degree. C. or higher, its adhesiveness is noticeably lowered. For example, if the temperature inside a car that has been parked outdoors in summer rises, thereby causing a decrease in the adhesiveness of the adhesive used, the hologram film will peel off the support plate, such as a windshield, etc. The thus-peeled film will be shrunk by the heat, and its optical characteristics will be changed. In such a case, the display image reproduced onto the hologram film will be deformed or unsharp thus lowering the quality of the reproduced image. In particular, when a hologram film is sealed in a windshield, two sheets of glass are hot-sealed under pressure at high temperatures whereupon the above-mentioned shrinkage of the hologram film is inevitable.